add descriptions and more tags for 18 YAML files

7 still missing descriptions, so reduce missing allowance to 7

Author: janosh

assets/disk-to-plane/disk-to-plane.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - string theory
   - topology
-description: null
+  - geometry
+  - complex analysis
+  - conformal mapping
+  - fundamental domain
+  - symmetries
+description: >-
+  Visualization of the Cayley transform S(w) = (w+i)/(iw+1) mapping the unit disk (D²) to the upper half-plane (H). The diagram shows how points and paths are mapped between these domains, with special points labeled. This conformal transformation is useful in string theory and conformal field theory, where calculations are often simpler in one domain than the other.

assets/ergodic/ergodic.yml

@@ -2,4 +2,10 @@ title: Ergodic
 tags:
   - physics
   - statistical mechanics
-description: null
+  - dynamical systems
+  - ergodicity
+  - phase space
+  - chaos theory
+  - trajectories
+description: >-
+  Phase space diagram showing two types of trajectories in a 2D oscillator system: a non-ergodic trajectory R (in red) for rational frequency ratio ω = 2 which forms a closed orbit, and an ergodic region R (in orange) for irrational frequency ratio ω ∉ ℚ which densely fills the available phase space P (blue ellipse). The diagram illustrates how ergodicity depends on the rationality of frequency ratios.

assets/feynman-diagram-1/feynman-diagram-1.yml

@@ -2,4 +2,9 @@ title: Feynman Diagram 1
 tags:
   - physics
   - quantum field theory
-description: null
+  - Feynman diagrams
+  - propagators
+  - Green's function
+  - effective action
+description: >-
+  Basic Feynman diagram showing a dressed propagator (hatched vertex) connecting two external fields φₐ and φᵦ with incoming momentum p₁ and outgoing momentum p₂. The vertex represents the full momentum-dependent two-point Green's function G_k, which includes all quantum corrections. This is a fundamental building block for more complex quantum field theory calculations.

assets/feynman-diagrams-loop-regulator/feynman-diagrams-loop-regulator.yml

@@ -9,7 +9,7 @@ description: |
 tags:
   - physics
   - quantum field theory
-  - feynman diagrams
+  - Feynman diagrams
   - loop corrections
   - propagators
   - quantum fluctuations

assets/gravitons/gravitons.yml

@@ -2,4 +2,9 @@ title: Gravitons
 tags:
   - physics
   - quantum field theory
-description: null
+  - particle physics
+  - gravity
+  - string theory
+  - Feynman diagrams
+description: >-
+  Feynman diagrams showing graviton interactions in quantum gravity, illustrating why gravity is difficult to quantize. Unlike other fundamental forces, graviton self-interactions lead to infinitely many terms of increasing complexity, resulting in the non-renormalizability of gravity and motivating the need for theories like string theory.

assets/matsubara-contour-1/matsubara-contour-1.yml

@@ -3,5 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: |
-  Complex contour plot illustrating a Matsubara summation. Used in thermal quantum field theory to compute Feynman diagrams at non-zero temperature. $C$ surrounds the imaginary $p_0$-axis counterclockwise but excludes poles of $(-p_0^2 + x^2)^{-1}$.
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  Initial contour C for evaluating Matsubara frequency sums. C runs counterclockwise around the imaginary p₀-axis where the Matsubara frequencies ωₙ = 2πn/β lie, but excludes the poles of the propagator 1/(-p₀² + x²). The integrand includes the Bose-Einstein distribution which has simple poles at all Matsubara frequencies with residue T.

assets/matsubara-contour-2/matsubara-contour-2.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: Deformation of contour $C$ in [Matsubara contour 1](https://janosh.github.io/diagrams/matsubara-contour-1) into a circle followed by taking the radius to infinity. This will enclose the poles of $(-p_0^2 + x^2)^{-1}$ scattered throughout the complex plane. Their contribution is removed again by enclosing them in clockwise contours.
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  First deformation of the Matsubara contour in https://diagrams.janosh.dev/matsubara-contour-1 where C is expanded into a circle followed by taking the radius to infinity, plus two small clockwise circles C₁ and C₂ around the propagator poles. Since the integrand falls off faster than 1/p₀, the contribution from the large circle vanishes at infinity, leaving only the pole contributions. The small circles around the poles are there to remove again the contribution from the poles that was added by enclosing them in the counterclockwise contour C.

assets/matsubara-contour-3/matsubara-contour-3.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: null
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  Second deformation of the Matsubara contour where the small circles C₁ and C₂ are expanded to enclose the entire complex plane except for the imaginary axis. This contour picks up both pole and branch cut contributions from the propagator, with the branch cuts arising from the sign function s(p₀).

assets/matsubara-contour-4/matsubara-contour-4.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: null
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  Special contour Cᵦ used to isolate branch cut contributions in Matsubara frequency sums. The contour runs along both sides of the real axis where the sign function s(p₀) changes discontinuously, giving rise to branch cuts in the propagator. This allows separating pole and branch cut contributions.

assets/matsubara-contour-5/matsubara-contour-5.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: null
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  Integration contours used to evaluate bosonic Matsubara frequency sums in thermal field theory. The diagram shows contours C₁ and C₂ (enclosing the complex plane except an infinitesimal slice along the imaginary axis where the Matsubara frequencies lie). This contour deformation technique converts discrete frequency sums into continuous complex integrals via the residue theorem.

assets/matsubara-contour-deformation/matsubara-contour-deformation.yml

@@ -3,4 +3,10 @@ tags:
   - physics
   - quantum field theory
   - Matsubara
-description: null
+  - complex analysis
+  - Green's function
+  - thermal field theory
+  - contour integration
+  - frequency sums
+description: >-
+  Visualization of contour deformations used in evaluating Matsubara frequency sums. The diagram shows how the original contour along the imaginary axis can be deformed to separate contributions from poles and branch cuts, allowing systematic evaluation of thermal correlation functions.

assets/operator-orderings/operator-orderings.yml

@@ -2,5 +2,9 @@ title: Operator Orderings
 tags:
   - physics
   - quantum field theory
-  - renormalization
-description: null
+  - causality
+  - Green's function
+  - time ordering
+  - propagators
+description: >-
+  Visualization of different operator orderings in quantum field theory: time-ordered, retarded, advanced, and symmetric Green's functions. The diagram shows how these orderings relate to different boundary conditions  to illustrate the connection between causality and propagator types.

assets/plane-to-torus/plane-to-torus.yml

@@ -2,4 +2,11 @@ title: Plane to Torus
 tags:
   - physics
   - string theory
-description: null
+  - topology
+  - geometry
+  - fundamental domain
+  - periodicity
+  - symmetries
+  - compactification
+description: >-
+  Visualization of how a rectangular region of the plane becomes a torus through periodic boundary conditions. The diagram shows the identification of opposite edges and the resulting fundamental domain, a key concept in string theory compactification where spatial dimensions are "curled up" into compact geometries. This construction helps understand modular transformations and the origin of winding modes in string theory.

assets/qft-propagator-poles/qft-propagator-poles.yml

@@ -2,5 +2,10 @@ title: QFT Propagator Poles
 tags:
   - physics
   - quantum field theory
+  - complex analysis
+  - Green's function
+  - propagators
+  - causality
   - Matsubara
-description: null
+description: >-
+  Complex plane visualization of propagator poles and branch cuts in quantum field theory. The diagram shows the analytic structure of Green's functions, including the relationship between retarded/advanced propagators and the placement of poles relative to the real axis. This structure helps understand causality and the connection to Matsubara frequencies.

assets/qft-propagators/qft-propagators.yml

@@ -6,4 +6,5 @@ tags:
   - causality
   - Green's function
   - Feynman
-description: null
+description: >-
+  Complex plane visualization of different propagator types in quantum field theory: retarded, advanced, and Feynman propagators. The diagram shows their analytic structure in relation to Matsubara frequencies (dots on imaginary axis). This representation helps understanding causality in quantum field theory and the connection between real-time and imaginary-time (thermal) formalisms.

assets/regular-vs-bayes-nn/regular-vs-bayes-nn.yml

@@ -2,6 +2,9 @@ title: Regular vs Bayes NN
 tags:
   - machine learning
   - neural networks
+  - Bayesian
   - statistics
+  - deep learning
   - probability
-description: null
+description: >-
+  Comparison between regular neural networks and Bayesian neural networks. The diagram illustrates how Bayesian networks incorporate uncertainty in their predictions by treating weights as probability distributions rather than point values, leading to more robust predictions with uncertainty estimates.

assets/torus-fundamental-domain/torus-fundamental-domain.yml

@@ -2,4 +2,10 @@ title: Torus Fundamental Domain
 tags:
   - physics
   - string theory
-description: null
+  - topology
+  - geometry
+  - modular invariance
+  - fundamental domain
+  - symmetries
+description: >-
+  The light gray-shaded areas show a fundamental domain of a torus under modular transformations. The diagram shows the region in the complex plane that uniquely parametrizes inequivalent tori, bounded by the modular projective special linear group PSL(2,Z) transformations that identify physically equivalent fundamental domains for the action of $\Gamma$ on the upper half-plane.

assets/torus/torus.yml

@@ -3,4 +3,9 @@ tags:
   - physics
   - string theory
   - topology
-description: null
+  - geometry
+  - fundamental domain
+  - symmetries
+  - periodicity
+description: >-
+  Three-dimensional visualization of a torus with major radius R and minor radius r. The torus is a fundamental geometric object in string theory, where strings can wrap around its two independent cycles. Its topology allows for periodic boundary conditions in two directions, which is relevant when studying compactification, modular invariance, and dualities in string theory.

scripts/check_yaml_files.py

@@ -231,5 +231,5 @@ def check_missing_descriptions(yaml_files: list[str]) -> list[str]:
     remove_duplicate_tags(yaml_files)
     missing = check_missing_descriptions(yaml_files)  # Add description check
     # TODO remove missing allowance once all diagrams have descriptions
-    raise_missing = len(missing) > 25
+    raise_missing = len(missing) > 7
     raise SystemExit(errors or raise_missing)  # Exit with error if any checks fail